Image sensors are widely used in digital still cameras, cellular phones, security cameras, as well as in, medical, automobile, and other applications. Complementary metal-oxide-semiconductor (“CMOS”) technology is used to manufacture cost effective yet high performance image sensors on silicon substrates. A large number of image sensors have the capability to sense both visible and near infrared (NIR) light. One application of such a sensor may be when used in an automotive sensor for driver assistance applications and safety applications, such as pedestrian, obstruction and sign detection, rear-view or back-up camera applications, etc. Such sensors can operate in a dual mode, which allows them to function both in daylight (in the visible light spectrum application) and night vision (in the IR application). This incorporated IR capability is made possible by the development and implementation of a number of process-level enhancements that expand the sensor's spectral light sensitivity to within the NIR range of 750-1400 nm.
For example, a typical image sensor that senses both visible light and IR light may include individual image sensor pixels, that are each configured to sense either visible or IR light. Those image sensor pixels that are configured to sense IR light typically include an IR pass filter to block light in the visible range and to only allow IR or NIR light to reach that pixel's photosensitive region (e.g., photodiode region). In some applications an IR pass filter is formed by stacking multiple color filters on top of each other (e.g., blue (B) and red (R)). Similarly, the image sensor pixels that are configured to sense the visible light typically include an IR cut filter that blocks IR or NIR light such that only visible light of a particular frequency range (e.g., Red (R), Green (G), or Blue (B)) reaches that pixel's photosensitive region. However, the addition of IR cut filters and IR pass filters adds to the material costs, as well as the process costs of fabricating an IR/Visible image sensor on the very same silicon chip.